Does this look right for comparing large injector ISK per SP to that of cerebral accelerators?
Cost per SP = ISK cost / SP gain
Accelerator SP Gain = (primary + secondary/2) * (1 + Biology/5) * minutes = 1.5 * stat increase * 2 * duration in seconds / 60
— SP Gain @ Biology V —
Expert Cerebral Accelerator: 432,000 SP = 1.5 * 8 * 2 * 1,080,000 / 60 SP
Master-At-Arms Cerebral Accelerator: = 43,2000 SP = 1.5 * 10 * 2 * 86,400 / 60 SP
Large Skill Injector (50M<SP<80M): 300,000 SP
Large Skill Injector (80M<SP): = 150,000 SP
— Cost per SP @ Today —
Large Skill Injector (50M<SP<80M): 2333 ISK / SP = 700,000,000 ISK / 300,000 SP
Expert Cerebral Accelerator: 2,613 ISK / SP = 1,129,000,000 ISK / 432,000 SP
Master-At-Arms Cerebral Accelerator: = 2983 ISK / SP = 128,900,000 ISK / 43,200 SP
Large Skill Injector (80M<SP): = 4667 ISK / SP = 700,000,000 ISK / 150,000 SP
In summary, injectors are cheapest up to 80M SP, after which point accelerators become cheaper. No surprise. Before working through the math, I had heard this.
Also, it looks like constantly running Master-At-Arms Cerebral Accelerators will give about 657,000 SP per month at a cost of about two billion ISK.
657,000 SP = 43,200 SP * (365 / 2) / 12
1,960,354,167 ISK = 128,900,000 ISK * (365 / 2) / 12